Hydraulic press



March 16, 1943.

H. FIELD, JR

HYDRAULIC PRESS Filed Dec. 22,' 19594 4 Sheets-Sheet 1 March 16, 1943.H. FIELD, JR 2,314,082"

HYDRAULIC PRESS I Filed Dec. 22, 1939 4 Sheets-Sheet 2 106 .107 Zjg'g- Z117 11811911524 1/ 5 90 A ,121 11 {-122 51 I g'wmm arch 16, 1943.

H. FIELD, JR

HYDRAULIC PRESS Filed Dec. '22. 1959 4 Sheets-Sheet 5 March 16, 1943..

' 1 H.'FI ELD, JR

HYDRAULIC 'PRESS Filed Dad. 22, 1939 4 Sheets-Sheet 4 Patented Mar. 16,1943 HYDRAULIC PRESS Howard Field, Jr., Los Angeles, Calif., assignor toNorth American Aviation Inc., Inglewood, Calif., a corporation ofDelaware Application December 22, 1939, Serial No. 310,546

Claims.

This invention relates to hydraulic presses, and particularly to pressesfor theforming of relatively thin sheet metal parts, such as areemployed, for example, in the fabrication of aeroplanes.

It is now a common practice in pressing thin sheet metal parts to employa male die on the bed of the press and a rubber matrix in the platenwhich presses the sheet metal aboutthe male die, thereby avoiding thenecessity of a rigid female die. Such a system requires extremely highpressures exceeding those commonly utilized with mating male and femaledies. Furthermore, a great amount of energy is stored in the compressedrubber, which energy is capable of throwing the platen up with dangerousforce and speed, if the closing force on the press is suddenly removed.

The present invention relates particularly to a hydraulic system forlarge presses of the type described, and has as a broad object toprovide automatic safety features that prevent the enormous forcesinvolved from getting out of control and causing injury either to thepress itself or to the person operating it.

Another object is to provide a control that is simple to operate and atthe same time automatically insures smooth movement of the press.

The foregoing objects, together with other more specific objects andfeatures of the invention will become apparent from the detailed description to follow of a. particular embodiment of the invention.

In the drawings: 7

Figure 1 is a schematic view of the hydraulic system of a press inaccordance with the invention; the view showing the ram in the upperposition and the control valve in the neutral or holding position.

Figure 2 is a schematic view of the ram' control valve and crackingvalve corresponding to the showing of these parts in Figure l, butshowing the valves in position for downward movement of the press.

Figure 3 is a schematic view, similar to Figure 2, but showing thevalves in position for moving the press upwardly at the beginning of theupward movement.

Figure 4 is a schematic view of the cracking valve showing the conditionof the valve during upward movement of the press through the upperportion of its stroke.

Figure 5 is a front elevation of the main control valve mechanism, ofwhich the presentinvention forms a part.

Figure 6 is a vertical sectional view through the main control valve forthe ram.

Figure 7 is an end elevation of a cracking valve for the ram.

Figure 8 is a vertical section through the cracking valve takensubstantially-on the line 8-8 of Figure 7.

Figure 9 is a longitudinal section through a safety control valve forthe ram.

Hydraulic system for the ram Referring to Fig. 1, there is shown ahydraulic system for actuating the head (not shown) of a press, whichhead is attached to a piston rod '1 of a ram piston I00 positioned inthe ram cylinder 3 of the press. Although the details of the pressplaten are notv shown, it is to be understood that the hydraulic systemherein to be described'is of particular usefulness in connection withthe type of press employing a compressible rubber platen for formingsheet metal around the male dies. The hydraulic system comprises, inaddition to the cylinder 3 previously mentioned, a main control valve80, a cracking. valve 8| which is automatic in its operation, a safetystop valve 82 which is likewise automatic in its operation, a pump 83, areservoir 84, a cooling device 85 and piping interconnecting thesevarious elements in proper relation. Thus fluid is delivered from thereservoir 84 through a pipe 86 to the pump 83 and thence through a pipe81 to the main control valve 80, from which it may flow to the crackingvalve either through a pipe 88 or a pipe 89, depending upon the positionof the valve 80. Fluid can flow between the cracking valve 8| and theupper end of the cylinder 3 through a pipe and between the main valve80, the cracking valve SI and the lower end of the cylinder 3 throughthe pipe 89. Fluid flow between the pipe 89 and the lower end of thecylinder 3 can only-occur through the safety valve 82.

The valve 82 will open in response to pressure in, either line 89 or 90but is always closed when no pressure exists in either of these lines.Thus the valve comprises a cylinder 9! in which a piston 92 isreciprocable between a left position, as shown in Fig. 1, in which itcovers a port 93 leading to the lower end of the-ram cylinder 3 and aright position in which it is displaced to the right of the port 93permitting communication of this port through the cylinder 9| with thepipe 89. The valve piston 92 is normally urged into the left positionshown in Fig. 1 by a spring 94. At its left end the cylinder 9|communicates with a smaller cylinder 95 containing a piston 96 connectedto the piston 82. The left end of the cylinder 85 communicates with alarger cylinder 95a, which is connected, by a pipe 91, with the upperend of the ram cylinder 3.

A piston 95b is fitted in cylinder 95a and has a short rod 950 extendingtherefrom and adapted to contact the piston 90. The right end ofcylinder 9i and the interconnected ends of cylinder 95 and 95a arevented through ducts Sid and 9501, respectively.

When no pressure exists in either pipe 09 or pipe 90, the spring 94controls the piston 92 and holds it in position to close the port 93, sothat fluid cannot escape from the underside of the ram piston I and thepiston is prevented from moving down in response to its own weight andthe weight of the press parts connected thereto through the piston rodI. However, if sufiicient pressure is developed in either the pipe 89 orthe pipe 97, force is exerted on the left end of piston 02 or the leftend of piston 35b to move the pistons to the right, uncovering the port93 and permitting fluid to flow to or from the lower end of the ramcylinder 3 under the control of valves 80 and 8|.

The construction and operation of the control valve 80 and the crackingvalve 8| will now be described. Under normal operation the pump 83 runscontinuously and when the control valve 80 is in neutral position, asshown in Fig. 1, fluid is circulated from the pump 83 through the pipe81 into a cylinder IOI in valve 80 between two valve pistons I02 andI03, respectively. This fluid flows directly through the cylinder IOIand out through a port I04 into a cylinder I05 between two valve pistonsI06 and W1 therein. Both of these pistons I06 and I0'I have openingslongitudinally therethrough so that fluid flowing through the port I04can escape through the piston I01 and thence through a return pipe I08back to the cooling device 85 and thence through a pipe I09 to thereservoir 84 from which it can again flow to the pump 83.

It will be observed, therefore, that with the control valve 80 inneutral position, as shown in Fig. 1, fluid from the pump 83 circulatesfreely through the valve 80 to the return pipe I08 and no pressure isdeveloped in the system. At the same time the pipes 88 and 89 are closedby the valve pistons I03 and I02, respectively, so that no pressurefluid is applied to either pipe 89 or 00 and the safety valve 02 remainsclosed, preventing downward movement of the ram piston I00.

It may be mentioned at this point that the function of the crackingvalve 8i is to control the initial upward movement of the ram pistonI00, following a pressing operation. The necessity of this valve arisesfrom the fact that the press employs a rubber matrix as the female dieelement, which matrix is highly compressed during each final downwardmovement of the press. As a result of the compression of the rubber,enormous energy is stored therein, tending to movethe piston I00upwardly and if the fluid in cylinder 3 above the piston I00 werepermitted to escape rapidly, the expansion of the rubber matrix in thepress would cause the piston to rebound with great velocity and force.Such rebound is controlled by the cracking valve BI which permitsonlyslow escape from the upper end of the cylinder 3 through the pipe 90until the energy stored in the compressed rubber matrix has beendissipated.

Let it be assumed, now, that the press is to be lowered, which operationis caused to be performed by rotating a control lever I48 about a shaftIIO on the valve clockwise into the position shown in Fig. 2. This movesthe piston I01 against the port I04, stopping free circulation ofpressure fluid from pipe 81 to the return pipe I08. At the same time thepistons I02 and I03 are moved to the right, clear of the ports of pipes89 and 88, respectively, so that pipe 88 is communicated with the supplypipe 8'! and pipe 89 is communicated (through the passages in thepistons I86 and I07) with the return pipe I08.

Pressure fluid, therefore, flows from pipe 81 into pipe 88, into thecracking valve 0i where it flows upwardly past the spring-actuated valveelement III, and through pipe 80 to the upper end of the ram cylinder 3.Pressure is therefore built up in the pipe 80 and in the .pipe 97(Fig. 1) which pressure acting upon the left end of the piston 96 in thesafety valve 82 moves the piston 92 clear of the port 93, permittingcommunication of the lower end of the ram cylinder 3 with the pipe 88.The application of the fluid under pressure through the pipe 03 to theupper end of the cylinder 3 moves the ram piston I00 downward, expellingthe fluid below the piston through the pipe 89 (Fig. 2) and through theopenings in the pistons I05 and I0! of the control valve 00 to thereturn pipe I 08. As the press closes with the ram piston I00 near thelower end of its stroke, the full pressure of fluid developed by thepump 83 is applied to the upper end of the piston and is maintained solong as the control lever I08 is maintained in clockwise position, asshown in Fig. 2.

When it is desired to restore the press to open position, the controllever I58 is rotated in counterclockwise direction from the positionshown in Fig. 2 into the position shown in Fig. 3. This connects thefluid supply pipe 8'! through the cylinder I0! to the pipe 89 andconnects the pipe 88 with the return pipe I08.

Fluid now flows freely from supply pipe 81 through the pipe 89, throughthe cylinder H0 in the cracking valve 8I, out through an open port I25in that cylinder, and past a check valve I26 and through a passage I23to the pipe 88, which is connected through valve 80 to the return pipeI08. Therefore no pressure is developed in the line 89.

At this time of course the piston I00 is being urged upwardly by theforce of the compressed rubber matrix in the press, but it can moveupwardly only as fluid is discharged from the upper end of cylinder 3through the pipe 90, and (Fig. 3), the only path for escape of fluidfrom the pipe 30 to the return pipe I88 is through the cracking valve8!, which now functions to perform its intended purpose of limiting therate of escape of fluid from the pipe 90 to the pipe 83 and thencethrough the control valve 80 to the return pipe I08.

It will be observed from an inspection of Fig. 3 that the pipe 90communicates with a passage IE2 which connects with the upper end of thepassage H3 leading to the valve element III and also communicates with avalve cylinder H4 through a port H5 and with the upper end of a cylinderIE5. The pressure fluid in the pipe 90 acts against the upper end of apiston II? in the cylinder H8, holding the latter in lowermost position,in which piston II'I closes a port H8 leading to the left end ofcylinder Hi. This prevents application of pressure fluid to the left endof cylinder H4 and pistons H9 and I28 in cylinder H4 are maintained inleftmost position by a spring IZI. In this position of pistons H9 andI2!) the latter :piston closes a port I22 leading to the passage I23 and'pipe 88. It will be apparent, therefore, that fluid cannot escape frompipe 90 through either port H or through the cylinder H8. The onlyescape is through the passage H3 past the valve element III and throughthe passage I23 into the pipe 88. The flow of fluid downwardly past thevalve element III aids a spring I24 in keeping the element in lowermostposition, in which it almost, but not quite, closes the passage H3 andfluid slowly flows out through the pipe 9! into the :pipe 88 and to thereturn pipe I98, permitting the ram piston I90 to slowly rise inresponse to the reactive force of the rubber matrix in the press.

During this stage of operation, the piston I I1 is maintained in lowerposition by the pressure of the fluid in' pipe 99 and passage H2, inwhich position pipe 89 is communicated through cylinder H6 and the portI25 thereof with the check valve I26, as previously described.

During this initial upward movement of the ram piston I60 the pressureof the fluid in pipe 90 applied through the pipe S'I-(Fig. 1) to theleft end of the piston 98 of the safety valve 82 holds the valve in openposition, in which pipe 89 is in communication with the ram cylinder 3.However, as previously indicated, the fluid supplied to pipe 89 is beingbypassed through the cracking valve BI so that the only force acting tomove the ram piston IBII upwardly is the reactive force of the rubber inthe press. This reactive force of the rubber in the press is graduallyreduced as the rubber expands to its normal size with the upwardmovement of the pisten; the force tending to lift the piston decreases,and the pressure of the fluid in the upper end of the cylinder 3 and inthe pipe 80 diminishes to a value insuflicient to maintain the piston II1 (Fig. 3) in lower position against the reactive force of a spring I28bearing against the lower end of the piston. Therefore piston I I1 ismoved into uppermost position, as shown in Fig. 4, in which the lowerend of piston III closes off port I25 and the upper end of the piston isclear of the port H8. Closure of the port I25 stops the free circulationof fluid from pipe 89 past the check valve I26 back to pipe 38 so thatthe pres sure rises in pipe 89. At the same time pipe 89 is connectedthrough port H8 with the left end of cylinder H4, moving the pistons II9 and I20 therein to the right against the force of the spring I2! andinterconnecting the port H5 with the port I22. This provides a freeconnection through passage H2 and cylinder H4 to the passage I23 andpipe 88 so that fluid in the upper end of the ram cylinder 3 may befreely evacuated during the remainder of the upward stroke of the rampiston.

Referring now to Fig. 1, the closure of the return path from pipe 89causes pressure to be developed in the pipe 89, which pressure, actingupon the safety valve 82, opens the latter to communicate pipe 89 withthe lower end of the ram cylinder 3. Pressure fluid is thereforesupplied to the ram cylinder to lift the piston Hill to the upper end ofits stroke, whereupon the operator moves the control shaft III) intoneutral position, as shown in Fig. 1, completing a cycle of operations.

Structural details of the system The control lever I46 (Fig. 1) of theram control valve 80 is manually actuated by means of a lever soarranged as to move in the same direction as the press element which itcontrols.

Thus referring to the elevation view of Fig. 5, the ram control valve 80is actuated by a lever I3I movable vertically. Downward movement oflever I3I causes the press platen to move downwardly, and upwardmovement of lever I 3| causes the press platen to move upwardly. Thisgreatly" reduces the possibility of the operator becoming confused inhis manipulation of the control lever v The ram control lever I3I (Figs.5 and 6), is fulcrumed on a standard I40 and cooperates with a sectorI4I having a notch I42 correspond-' ing to the neutral position ofoperation and cooperating with a detent I43 on the lever I3I. The leveris positioned above the case of the ram control valve 80 and at its rearend is con-, nected by a linking rod I 45 with a bellcrank lever; I46which is pivotally mounted on the shaft H0 and has lower and upperextremities connected by links I48 to rods I49 and I50, respectively,

which rods extend into the casing of the valve; 30. The rod I59 carriesthe pistons I02 and H13 Fig. 1.

The safety valve 82, previously described with reference to theschematic view of Fig. 1, is mounted directly upon the ram cylinder andmay be constructed as shown in Fig. 9, in which corresponding elementsbear the same reference numerals as in Fig. 1.

It is to be understood that for the purpose of explaining the invention,the construction and operation of a particular embodiment thereof hasbeen described in detail, but the invention is not necessarily limitedto the particular construction described, except to the extent set forthin the appended claims.

I claim:

1. In combination with a hydraulic press having a ram cylinder and apiston therein movable from a first end of said cylinder to a second endthereof to close said press, a pump, fluid connections from said pump tosaid cylinder including a first conduit extending from said first end ofsaid cylinder, and a second conduit extending from said second end ofsaid cylinder, control means for selectively connecting the output ofsaid pump to either one of said conduits and connecting the otherconduit to a source of fluid for the intake of said pump; and meansresponsive to pressure in said one end of said cylinder for throttlingthe discharge of fluid from said cylinder through said first conduitwhile said pressure is in excess of a predetermined value, and permitting free discharge through said conduit' when said pressure is belowsaid predetermined value.

2. In combination with a hydraulic press having a ram cylinder and apiston therein movable from a first end of said cylinder to a second endthereof to close said press, a pump, fluid connectionsfrom said pump tosaid cylinder including a first conduit extending from said first end ofsaid cylinder, and a second conduit extending from said second end ofsaid cylinder, control means for selectively connecting the output ofsaid pump to either one of said conduits and connecting the otherconduit to a source of fluid for the intake of said pump, means forthrottling discharge of fiuid from said one end of said cylinder throughsaid first conduit, and means jointly responsive to decrease in pressurein said one end of said cylinder and to the flow of fluid from said pumpthrough said second conduit for providing a by-pass passage through saidfirst conduit past said throttling means.

3. In combination with a hydraulic press having a ram cylinder and apiston therein movable from a first end of said cylinder to a second endthereof to close said press, a pump, fluid connections from said pump tosaid cylinder including a first conduit extending from said first end ofsaid cylinder, and a second conduit extending from said second end ofsaid cylinder, control means for selectively connecting the output ofsaid pump to either one of said conduits and connecting the otherconduit to a source of fluid for the intake of said pump, meansresponsive to pressure in said one end of said cylinder in excess of apredetermined value for throttling the discharge of fluid from saidcylinder through said first conduit, and means jointly responsive todecrease in pressure in said one end of said cylinder, and to the flowof fluid from said pump through said second conduit for providing abypass passage through said first conduit past said throttling means.

4. The combination as described in claim 1, said last mentioned meanscomprising a checkvalve permitting free flow of fluid through said firstconduit to said first end of said cylinder and permitting restrictedflow therefrom.

5. In combination with a hydraulic press having a ram cylinder and apiston therein movable from a first end of said cylinder to a second endthereof to close said press, a pump, fluid connec tions from said pumpto said cylinder including a first conduit extending from said first endof said cylinder, and a second conduit extending from said second end ofsaid cylinder, control means for selectively connecting the output ofsaid pump to either one of said conduits and the other conduit to asource of fluid for the intake of said pump, means responsive topressure in said one end of said cylinder in excess of a predeterminedvalue for short-circuiting fluid flow from said pump through said secondconduit to said first conduit, said means including a check-valve forpreventing short-circuiting flow of fluid in the reverse directionthrough said first conduit to said second conduit.

HOWARD FIELD, JR.

